1. Field of the Invention
This invention relates generally to storage and dispensing systems for the selective dispensing of a gas from a storage and dispensing vessel containing a physical sorbent medium, on which the gas has been sorbed, and from which the gas is desorbed in the dispensing operation. The invention further relates to semiconductor manufacturing systems and processes utilizing such storage and dispensing systems for reagent delivery, to electronic device structures obtained by such semiconductor manufacturing processes, and to end use products including such electronic device structures.
2. Description of the Related Art
In a wide variety of industrial processes and applications, there is a need for a reliable source of process fluid(s) which is compact, portable, and available to supply the process fluid(s) on demand. Such industrial processes and applications include semiconductor manufacturing, ion implantation, manufacture of flat panel displays, medical treatment, water treatment, emergency breathing equipment, welding operations, space-based applications involving delivery of liquids and gases, etc. The aforementioned needs are particularly acute in the semiconductor manufacturing industry, due to progressively increasing electronic device integration densities and increasing wafer sizes, which demands a high level of process reliability and efficiency.
U.S. Pat. No. 4,744,221 issued May 17, 1988 to Karl O. Knollmueller discloses a method of storing and subsequently delivering arsine. In the disclosed method of this patent, arsine is contacted at a temperature of from about -30.degree. C. to about +30.degree. C. with a zeolite of pore size in the range of from about 5 to about 15 Angstroms to adsorb arsine on the zeolite. The arsine is subsequently dispensed by heating the zeolite to an elevated temperature of up to about 175.degree. C. for sufficient time to release the arsine from the zeolite material.
The method disclosed in the Knollmueller patent is disadvantageous in that it requires the provision of heating means for the zeolite material, which must be constructed and arranged to heat the zeolite to sufficient temperature to desorb the previously sorbed arsine from the zeolite in the desired quantity.
The use of a heating jacket or other means exterior to the vessel holding the arsine-bearing zeolite is problematic in that the vessel typically has a significant heat capacity, and therefore introduces a significant lag time to the dispensing operation. Further, heating of arsine causes it to decompose, resulting in the formation of hydrogen gas, which introduces an explosive hazard into the process system. Additionally, such thermally-mediated decomposition of arsine effects substantial increase in gas pressure in the process system, which may be extremely disadvantageous from the standpoint of system life and operating efficiency.
The provision of interiorly disposed heating coil or other heating elements in the zeolite bed itself is problematic since it is difficult with such means to uniformly heat the zeolite bed to achieve the desired uniformity of arsine gas release.
The use of heated carrier gas streams passed through the bed of zeolite in its containment vessel may overcome the foregoing deficiencies, but the temperatures necessary to achieve the heated carrier gas desorption of arsine may be undesirably high or otherwise unsuitable for the end use of the arsine gas, so that cooling or other treatment is required to condition the dispensed gas for ultimate use.
U.S. Pat. No. 5,518,528 issued May 21, 1996 in the names of Glenn M. Tom and James V. McManus, describes a gas storage and dispensing system, for the storage and dispensing of gases, e.g., hydride gases, halide gases, organometallic Group V compounds, etc. which overcomes various disadvantages of the gas supply process disclosed in the Knollmueller patent.
The gas storage and dispensing system of the Tom et al. patent comprises an adsorption-desorption apparatus, for storage and dispensing of gases, including a storage and dispensing vessel holding a solid-phase physical sorbent, and arranged for selectively flowing gas into and out of the vessel. A sorbate gas is physically adsorbed on the sorbent. A dispensing assembly is coupled in gas flow communication with the storage and dispensing vessel, and provides, exteriorly of the vessel, a pressure below the vessel's interior pressure, to effect desorption of sorbate from the solid-phase physical sorbent medium, and flow of desorbed gas through the dispensing assembly. Heating means may be employed to augment the desorption process, but as mentioned above, heating entails various disadvantages for the sorption/desorption system, and it therefore is preferred to operate the Tom et al. system with the desorption being carried out at least partially by pressure differential-mediated release of the sorbate gas from the sorbent medium.
The storage and dispensing vessel of the Tom et al. patent embodies a substantial advance in the art, relative to the prior art use of high pressure gas cylinders, as for example are conventionally employed in the semiconductor manufacturing industry to provide process gases. Conventional high pressure gas cylinders are susceptible to leakage from damaged or malfunctioning regulator assemblies, as well as to rupture and unwanted bulk release of gas from the cylinder if the internal gas pressure in the cylinder exceeds permissible limits. Such overpressure may for example derive from internal decomposition of the gas leading to rapidly increasing interior gas pressure in the cylinder.
The gas storage and dispensing system of the Tom et al. patent thus reduces the pressure of stored sorbate gases by providing a vessel in which the gas is reversibly adsorbed onto a carrier sorbent, e.g., a zeolite, activated carbon and/or other adsorbent material. Considering now the manufacture of semiconductors in greater detail, many processes used in semiconductor manufacture utilize hazardous materials, e.g., toxic, flammable or pyrophoric, in the vapor state. The safety of the manufacturing process in various instances could be significantly improved by replacing the currently used gas sources. In particular, hexamethyldisilazane (HMDS) and chlorotrimethylsilane (CITMS) are used as primers to increase the adhesion of photoresists to wafers. HMDS and CITMS can be spun on the wafer but are typically applied either as a spray or a vapor. Photoresist developers and strippers are normally used as liquids but can also be used as vapors; these materials are acids or bases (organic or inorganic) and can have aromatic functionality. The safety of use of all these materials could be improved from their current mode of supply and usage in the semiconductor manufacturing facility.
In general, the manufacture of semiconductors requires very low contamination levels. Typical manufacturing facilities yield completed wafers with defect densities of a few tenths/cm.sup.2. Maintaining the cleanliness of the tooling is essential to realizing a process flow at competitive costs. In-situ chamber cleans are now routine for most process tools. Many of the gases or high vapor pressure liquids used in these cleans are hazardous, exhibiting one or more of the following properties: toxicity, flammability, pyrophoricity and/or adverse impact on the ozone layer (by so-called global warming gases). The safety of the cleaning processes could be significantly improved by replacing the gas sources currently employed.
In addition to the aforementioned cleaning reagents, many other process gases used in the manufacture of semiconductors are hazardous and exhibit one or more of the following properties: toxicity, flammability or pyrophoricity. In particular, chemical vapor deposition processes (CVD) are carried out with gaseous or liquid feed stocks which in many instances are associated with significant health and safety issues. Such gases are essential to create the individual layers making up the semiconductor structure, but the safety of the manufacturing process could be significantly improved by replacing the fluid sources utilized in current conventional semiconductor manufacturing practice.
A serious problem with storage and dispensing systems of the general type described in U.S. Pat. No. 5,518,528 is decomposition of the stored gas, such as hydride gas species. The '528 patent attempts to minimize the problems associated with generation of decomposition products of the stored gas, by utilizing sorbent materials containing very low levels of the trace materials which can catalyze or mediate decomposition reactions such as the degradation of arsine to form hydrogen gas. Hydrogen gas is flammable and has an associated safety risk, as well as increasing the pressure of the stored gas beyond desired levels (of atmospheric or near-atmospheric pressure).
Since variation in sorbent material may occur as a result of manufacturing, storage conditions, etc., and since in some instances it may be desirable to utilize more economic grades of sorbent material, it would be desirable to provide a gas storage and dispensing system which has such flexibility, without the deleterious effects incident to gas decomposition.
It therefore is an object of the present invention to provide a gas storage and dispensing system, and associated semiconductor manufacturing apparatus, systems and methodology which overcome the various aforementioned deficiencies of the art.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.